It is known that concrete slurry can be prepared for use in one location, which can be remote from the place of its intended use, and then conveniently transported by known means, such as in a truck, to the place of its intended use. It is also known that concrete slurry can be prepared while being transported to the intended place of use. A truck ordinarily employed to transport concrete slurry is referred to in the art as a ready mix truck.
The movement of concrete sometimes and typically has a critical phase, that of concrete being placed without costly time delays to contractors. Concrete contractors rely on concrete pumpers to make sure the concrete is placed where they have a continuous flow without the above mentioned time delay. The time delay may have a detrimental effect on the concrete and weaken the concrete and may cause the concrete contractor to have to replace a previously poured slab or high rise, high way pillar, etc. Contractors use concrete trucks to facilitate the movement of slurries through the use of a pump and a hopper built directly into the truck.
When concrete slurry is delivered to the intended location of use, it is known that it can be caused to flow by gravity or by pumping into a form where, because of its fluid condition, it conforms to the shape of the form. After the concrete slurry is in the form it is permitted to remain undisturbed therein for a period of time sufficient to enable the cementitious material to hydrate to thereby produce the set concrete.
One of the problems involved in the placement of concrete slurry concerns the potential difficulty of causing the slurry to flow through a conduit. In this regard, it is sometimes necessary, or otherwise convenient, to place the slurry in the desired form by pressuring it, by means of a pump, through a conduit over a distance to the desired form. However, due to the nature of a concrete slurry, it has sometimes been found essential, in order to initiate movement of a slurry to and through the pump and conduit, to first fill the pump with a fluid which is easily pumped and which will lubricate the conduit itself, followed by pumping such fluid ahead of the slurry. This process is referred to as priming. Attempting to pump concrete without using a lubricant or coating of some kind could result in a very costly delay.
The prior art has addressed the problem of priming a concrete slurry pump by employing methods featuring the use of two different compositions, one of which is called a “priming grout mix” and the second of which is called a “priming slurry.” The methods of priming a concrete slurry pump with either a priming grout mix or a priming slurry, as heretofore employed, are similar and suffer a common disadvantage. The disadvantage originates from the fact that the concrete slurry being pumped is not compatible and cannot be admixed with either one of the prior art priming compositions because any such admixture adversely affects the strength of the set concrete. Accordingly, when employing either one of the prior art methods, the delivery end of the conduit cannot be placed in the form until all of the priming composition has exited therefrom in order to avoid any admixing of slurry and priming composition.
Because the prior art compositions cannot be admixed with the concrete slurry, as explained above, the priming compositions must be directed to and placed in a separate location to enable hydration and subsequent disposal thereof. Accordingly, a waste disposal and potential environmental hazard inherently accompanies the use of prior art priming compositions.
Thus one problem to be solved in the prior art is to devise a composition for and a method of priming a concrete slurry pump which will not only permit a slurry to be successfully pumped, but which will also avoid the waste disposal and environmental problems associated with methods currently employed.
A priming grout mix usually consists of concrete sand, hydraulic cement and water in the weight ratio of 10 to 2 to 1, respectively. In typical practice about one-half cubic yard of priming grout mix is placed in a ready mix truck which then transports the mix to the location of the concrete slurry pump, which is ordinarily a positive displacement pump. The mix is there employed to prime the pump in order to cause a concrete slurry to move through the pump and conduit to the desired form. In the example just cited, one-half cubic yard of priming grout mix includes about 1500 pounds of sand, 300 pounds of dry cement and 150 pounds of water. In view of the fact that a ready mix truck ordinarily holds at least about 8 cubic yards of material, it is apparent that a truck employed to transport a priming grout mix is dramatically under-utilized in that it is solely used to transport a material which cannot be added to the concrete slurry.
A priming slurry typically consists of one bag of hydraulic cement dispersed in 6 or 7 gallons of water. As used herein, a bag of cement weighs about 94 pounds. Since a gallon of water weighs about 8.33 pounds, the weight ratio of cement to water in a typical priming slurry is an amount in the range of from about 1.6 to about 1.9 pounds of cement per pound of water. In practice about one-half of the required cement and water is thoroughly mixed and added to a hopper, which is in direct fluid communication with the suction side of the concrete pump, thereafter the balance of the cement and water is thoroughly mixed and added to the hopper prior to the initiation of pumping. Although use of a priming slurry does not involve an extra ready mix truck, as is required in the case of a priming grout mix as described above, it is required that extra bags of dry cement be transported to the pump location to enable on-site preparation of the priming slurry.
Another prior art method set forth in U.S. Pat. No. 5,997,633, incorporate herein by reference, involves a composition comprised of a water soluble, inorganic, alkaline material in combination with a solvatable, organic, polymeric material, when mixed with a quantity of water sufficient to dissolve the alkaline material and solvate the polymeric material. This method has the disadvantage of the dry material is hard to uncoil and absorbs and takes on water, particularly if the water is cold. Also the prior art composition includes alkaline material as added fillers, which may also continue to hydrate and present other problems associated with alkalinity. The product is also bulky and expensive to ship to customer. Customers must mix on site and allow time for the mixture to be prepared and soluble. Similarly, in WO 2005/073556, an eight ounce bag of dry composition is used, which then has to be placed in a five gallon container of water, and stirred for several minutes (or longer) so the product can uncoil, which sometimes never uncoils. A further problem with dry compositions is that it is very difficult to remove from one's hands, particularly if one's hands are wet.
Thus, the prior art solutions all suffer from the same basic problem, i.e., they start with a solid composition. As noted above, solid compositions tend to be relatively heavy, and usually require mixing for a period of time on site. Solid compositions also tend to continue hydrating. In addition, some of the particulate material used in the solid compositions tends to travel to undesirable locations either within the concrete machinery or onto the people operating the concrete pumping equipment.
On the contrary, the priming agent of the present invention does not start with a solid particulate-based composition, but instead starts with a liquid composition that overcomes the above-mentioned prior art problems associated with solid compositions. The present inventor has found that the liquid composition of the present invention is fast and effective on immediate contact with water, wets out on contact and can be sold in concentrate form, which reduces packaging weight, size and shipping costs to the customers. A liquid product also decreases wear on equipment, promotes ease and range of pumpability, is easily primed into the hopper and pumping equipment, creates a slick lubricant that reduces pressure and friction on lines and concrete pumping tubes, enhances slipperiness and thickness and viscosity of the pumping aids, coats pump wall lines for longer periods of pump time without continued hydration, and delivers lubrication and coating every time with a liquid emulsion. With the use of a liquid composition, there are also no hydration problems commonly associated with primers that start with solid compositions. It is therefore an object of the present invention to improve on the prior art through the use of a liquid polymeric emulsion as a primer aid or lubricant coating for a concrete pump system and delivery conduit.